Insulation v Conservation – Finding a solution

Brentham News Extra (see below) clarifies the Brentham Society’s position in relation to double glazing. Reference is made to two recent Planning Inspectorate Appeal decisions which can be read here. We welcome your comments.

13 Responses to Insulation v Conservation – Finding a solution

As noted in Brentham News 183 (June 2015) the Brentham Society has already set up a working group to look at ways to find standard double glazed windows that can be discussed with the Council Conservation Officer to see if the Area Plan can be suitably amended. Currently the Area Plan does not allow double glazing on front elevations unless it replaces non standard windows and would thus be an improvement. Please note once again that it is the Council that writes the Area Plan, not the Brentham Society. It is essential that, if double glazing is to be allowed, there is a standard set so that it does get installed in a piecemeal and varied fashion

Having written to the Brentham News i was surprised to see my letter published.
The result of this is That several people have knocked on my door
To discuss the issue of double głazed windows and it is quite
Clear from these conversations that there is a ground swell
For change on this issue. The feeling is that the committee is out of touch
And are not exploring the issue . With energy costs rising it is not good enough
To sit tight and adopt an attitude that i f you don’t like it
Dont live here!
I believe we should call for an EGM to discuss this issue with a ballot
For sensible change

INSULATION VERSUS CONSERVATION – FINDING A SOLUTION.
As the agent involved in both the planning and appeal for 4 Denison Road I would like to address some of the points raised in the April Bentham Extra News, I am part of a bespoke joinery company that specializes in the manufacture and installation of traditional timber windows and doors for Listed Buildings and Conservation Areas. In addition our company also install secondary glazing and is therefore very much in the middle of the current debate.

Sample Test Window
This was installed at 4 Denison Road and was not listed or named as a standard approved Brentham Style window but simply a window made for that opening, based on the window designs common to that house, based on the original Brentham designs showing in neighbouring houses.
With regard to the comment that as a company we have issued marketing material referring to ‘the approved Brentham Style window’ I would like to clarify that this reference was relating just to 4 Denison Road as outlined above and perhaps on reflection should have been referred to as ‘An’ approved Brentham Style window rather than ‘The’ approved Brentham Style window’
The sample window was installed to help all concerned make an informed decision and to show how the profiles and dimensions of the double glazed window compared to the existing and original single glazed window design irrespective of the fact that it had the same window ‘symmetry’. If the profile, moulding and period detail is wrong it does not make the window symmetry right.

The Brentham Society’s View
As specialists in the field of windows and doors for Listed Building and Conservation Areas, we undertake both planning and appeal applications, consequently we are fully aware that each case has to be treated individually. As a bespoke timber Joinery Company in this market sector it is obviously in our interest to do so, be it for single, double or secondary glazing.
We agree that probably one of the most distinctive features seen on the front of the Brentham Garden Estate Houses are the windows and we are pleased to say for this Conservation Area it applies also to the back which is a rarity even in some of the Listed Building areas we have worked in.

On the question of the aesthetic features mentioned regarding Brentham window detail:
“Their appeal rests in the delicacy of the frames and glazing bars and the characteristic uneven reflections created by the original glass pane. They also serve to unite the overall appearance when houses are grouped in terraces. So changing the windows in a Brentham house will affect its ‘look’ and in many cases detract from the visual appeal of the street”.

I am slightly puzzled by the above when I observe many of the window frames, especially those south to west facing, that are either replacements or originals with spliced in timber sections, filler, replacement modern casement lights, failing paintwork and suffering from timber fibre degeneration. There are also glazing bars in similar condition with paint flooded into the putty shrinkage gaps in the hope of creating a weather seal. Replacement timber windows constructed in the modern style of storm-proof casements akin to the PVCu windows. Glazing bars of 27 mm widths instead of the 21 mm slim bars of the originals. The Brentham dummy transom glazing bar detail 80- 90 mm in depth as opposed to 75 mm. Many of the properties are bereft of even the slimmest shard of the original or crown glass but sport modern float glass. Some approved replacement timber windows are lacking the external period profile and detailing. All the approved windows with double glazing units, although to the sides, alleyways and extensions and back elevations of the properties, are fitted with silver or black spacers. There is also a serious adverse knock on effect of some impaired windows i.e. external wood sills with no drip grooves due to continuous ill-conceived repair work encouraging rainwater runoff directly onto/into the brickwork resulting in bricks flaking or spalling with frost erosion in both bricks and pointing. All that is just for Denison Road and three of those are sporting non Brentham style windows.

Perhaps the last sentence of the extract quoted above should be rephrased as follows:

“So changing the windows in a Brentham house will affect its ‘look ’and in most cases improve the visual appeal of the entire street”

Will affect its ‘look’
The inspectorate had this to say regarding the ‘look’ in his appeal decision APP/A5270/D/14/2220685 for No. 4 Denison Road:

Section 7
“Compared to the window to be replaced the new windows are similar in design and appearance …….. “

Section 8
“The appeal scheme would introduce a consistent design in the detailed fenestration of the building bringing with it a pleasing uniformity in appearance…..”

Section 10
“Overall, I consider that the intrinsic character of the host building would be maintained ….”

Section 11
“Therefore, I conclude on the main issue that the proposed development would be in keeping with the character and appearance of the host building and the local area. The character and appearance of the CA would be preserved…”

It may come as no surprise to the Brentham Society that a large number of BGE residents share the same views and conclusions as the Inspectorate.

In answer to the question raised by The Brentham News Extra: “So what can be done?” It may be an idea to consider what the owners of 4 Denison Road ‘have done’ and the criteria they put forward for the replacement of nine windows and one set of doors to their home as follows:

1. Five of the windows are 1980’s modern, degenerated storm-proof style casements similar to PVCu in their design, these are to be replaced with timber replicas of the original designs to bring uniformity of period Brentham design
2. Replace ‘bodged’ modern day storm-proof window to back first floor and redesign its symmetry to match the original adjacent designs and profiles (highlighted and acknowledged by The Inspectorate APP/A5270/D/142220685)
3. Install replacement windows fit for purpose and put an end to the continuous cycle of costly repairs to windows well past their prime and beyond further repair
4. Put a stop to the adverse knock on effect of the dysfunctional windows that are encouraging damage to the external brickwork
5. Provide easy to open windows with ventilation options, toughened safety glass which is important for the elderly and young and period style ironmongery with security locking
6. Address condensation mould problems with the introduction of double glazed sealed units, effective draught/weatherproof seals and varied ventilation options
7. Windows with low maintenance requirements for both the short and long term
8. Replacement back French style doors in the style of the Brentham period/profile detail
9. Both windows, doors and installations to be covered by insurance backed guarantee
10. A sample test double glazed window to be installed in the rear kitchen extension to be used as a bench mark of design and quality control

The owners of No. 4 Denison Road were insistent that the sample window had to follow the design ethos of the BGECA i.e. dimensions, proportions etc. it was pointed out to the owners, and later observed on the test window, that the only difference, other than the double glazing would be the overall window depth and glazing bars increased by 5mm (less than ¼ of an inch).

Double Glazing in Brentham Frames
It is possible to make up double glazed units with wavy period style glass which can mirror the characteristic uneven reflection common to the original glass panes (samples of this are available to view).

Obviously double glazing is thicker than single glazing and in the case of No. 4 Denison Road the glazing bar will be 5mm deeper to accommodate it. There are also other ways of installing the slim double glazing bars that provide the same aesthetic result and reduced U-values (samples available to view).

On the question of the energy used to produce these slim double glazed units; a similar issue could be raised regarding the manufacturing of aluminium frames used for secondary glazing. An aluminium window frame requires 45 times more energy to produce than a timber framed window.

U-values for double glazed slim units i.e. 12 or 14mm have centre pane U-values of 2.0 and 1.5 respectively, the latter complies with current building regulations Document Part L.

Although there are different schools of thought on fitting double glazed units in the original or replacement single glazed frames this should be advised against. If undertaken the existing main frame needs to be square and in perfect condition, even so it may be problematic to install effective draught/weatherproof seals and would require the need to slim down the stiles, bottom and head rails (about 2-3mm) of the casement lights to allow for the seals, this needs to be undertaken by a highly skilled joiner/glazier. It must be considered that when originally constructed the casement lights were made to take only 3 or 4mm single glazing by size and weight and not double glazing, particularly when they are now nearing 100 years old, distorted and in many cases tenuously held together with filler and spliced timber sections.

Routing out part of the original frame structure thus compromising the structural integrity of the frame to accommodate the thicker, heavier slim double glazing (2 x the weight) fixed with an external putty bead, could result in units failing sooner rather than later.

Our experience has shown that this mix of old and new is not the best joinery practice and is impossible to provide any realistic guarantee although considerable time and money are involved.

The Council’s Policy – The Way Forward
We are all aware of the Council’s policy however, in light of the current successful appeal for No. 4 Denison Road replacement double glazed windows would not detract from the visual appearance of the host building and street. Many original and replacement windows are now beyond realistic/meaningful repair and glazing and window construction/design is continuing to advance in a way that now needs to be considered.

With the above in mind a large proportion of Brentham residents I have encountered over the past months, feel that a more unified and pragmatic approach regarding approved replacements fitted with double glazing would be The Way Forward.

It has also been suggested by various BGECA homeowners that an action group/quality control body is set up to ensure full compliance for all window replacements be they single or double glazed. By adopting this approach it is hoped to:
a) Put an end to the ‘go it alone’ homeowners replacing windows and straying from the original design/period detail which results in incremental damage and could threaten the Article 4 Direction of the BGE.
b) Encourage uniformity and parity for all homeowners and help to maintain the Brentham ‘look’
c) Ensure compliance and provide a level playing field for all
d) Evaluate any new developments in glazing window construction in a more meaningful way i.e. arrange test/quality control samples, open forums

Two Recent Appeal Decisions
Your overview of the two appeals suggested “outcomes that seem inconsistent” and “contradictory appeal decisions”. In addition you go on to say “he focussed on the host building (i.e. for No. 4 Denison Road) in contrast to the other appeal (No. 21 Denison Road) where the focus was on the impact of the new windows on the terrace”

The above summaries of your overview seem to imply other agenda and may confuse some BGECA homeowners rather than enlighten them. It must be emphasised both appeals had exactly the same agenda which was summarised in each appeal section 3:

4 Denison Road – The main issue in this appeal is the effect of the proposed development on the character and appearance of the host building and the local area.

21 Denison Road – the main issue is the effect of the proposal on the character and appearance of the host dwelling and the BGCEA which is a designated heritage asset.

What appears to have been overlooked here is quite simply the fact that the proposed double glazed window for No. 4 Denison Road was in the first instance approved and was seen to comply with the main issue whereas that proposed for No. 21 was not, thus making the overview summary and remarks regarding its effect on the terrace etc. irrelevant.
We understand that each planning application is considered on a case by case basis however, there will be many more BGECA homeowners that can now view the appeal results based on the premise ……..

If the window for No. 4 is approved for both the host dwelling and the immediate local area, then it may follow that since No. 21 is in the immediate local area with similar windows, and even further back from the road than No.4, the difference would be even less “discernible”. So the approved windows for No. 4 will also be OK for No. 21 and others.

To summarise I would like to outline the issues that may have contributed to the successful appeal for No. 4

No.4 APPROVED No.21 REFUSED
No.4 Test/sample double glazed window following the Brentham period design installed to help the Inspectorate and whoever was viewing it
No.21 No test/sample window in the decision making although a sample was offered to the Ealing Council Planning Dept. which was not taken up.
No.4 Double glazing sample fitted with white warm edge spacers to blend in with window colour and profile and be more harmonious with the immediate local single glazed windows
No.21 Black spacer which may be considered to look like a double glazed black rubber gasket which would stand out from the local single glazed windows
No.4 Glazing bars and frame an extra 5mm deeper than for the original windows
No.21 Glazing bars and frame an extra 9 mm deeper than for the original windows
No.4 A window design change to the back first floor was proposed by us to improve ‘the look’, this was approved by the Inspectorate
No.21 No action

SECONDARY GLAZING
As well as single and double glazing, we are also able to install secondary glazing. However, this is mainly fitted to Grade II Listed Buildings where, for reasons of retaining the original fabric of the building, double glazing is not a choice.

It must be pointed out that secondary glazing does not perform in the same way as a double glazed sealed unit but in combination with the primary window as two panes of glass with an air gap between them. To install secondary glazing a timber sub frame is required otherwise the primary window should have timber reveal linings or architrave onto which the aluminium frame can be fixed, this aluminium frame in turn holds the aluminium framed movable pane of glazing.

Nowadays some secondary glazing has a low emissity coating similar to that used in double glazed units and there is now talk of using double glazed units with secondary glazing. Although it is considered as a solution for thermal insulation its main function was to help reduce sound transmission particularly if internally installed 4 inches (100mm) away from the primary (original) window glazing.

Unfortunately secondary glazing does receive a great deal of bad press because it is considered to be:
 Obtrusive and restricts direct access to the primary window
 Difficult to clean and harbours dust, dirt, flies etc.
 Fitted with modern aluminium or plastic frames that conflict with the period detail of a traditional timber window
 Difficult to gain easy and effective ventilation as there are two windows to negotiate
 Not very aesthetically pleasing as the secondary glazing frames etc. can be seen from both inside and out
 A problem to reduce condensation between the two panes of glass which can result in mould formation and restrict vision and light
 Two windows to maintain instead of one
 Does not comply with current building regulations regarding window replacement and heat energy conservation and thermal insulation. In the case of Grade I & Grade II Listed Buildings however, where replacement windows fitted with double glazed sealed units are not permitted, secondary glazing is proposed as a substitute.
 Overheating in south to west facing rooms (Green House effect) during the summer months
 Can be problematic for shutters, blinds and curtains
 For casement windows a loss of the internal sill space/for sliding box sash windows set back in the cut brick reveal it projects into the room and for some is considered more obtrusive
 Operating with torsion and spring balances which are prone to breaking down and dangerous when spring loses torsion as the glazing drops unrestricted with a guillotine like effect.
 A dilemma to invest in when the primary window is in total disrepair
 The aluminium frames fitted with no thermal breaks can encourage condensation around the secondary glazing edges which can also lead to mould formation

Tony Moore writes:
I don’t know who advised the Society regarding the thermal efficacy of slim double glazing units – in terms of the U Values they can achieve, the real savings they can realise and their comparative performance relative to good quality secondary glazing – but I’d like to know where he or she got their information from, as it does not reflect my understanding of the realities of the situation. There appears to be an element of scaremongering here. And by the way, the use of 12mm or 13mm Slim Units – which can achieve U Values of 1.5 or 1.4 – can be realised with casement and glazing bar depths of just 5mm greater than that applying to original single glazed Brentham Window assemblies, which is somewhat less than a quarter of an inch and not much more than the actual depth of many existing/original sections to Brentham Windows that have received a few coats of paint, which puts in context the misleading and creative assertions contained in the News Extra Broadsheet that glazing bars have to be much deeper to accommodate the units. You might also like to know that the leading manufacturers of slim double glazing units now offer 10 year guarantees for their wares.

The subjective arguments and assertions propounded by the Society regarding the appearance of double glazing panels relative to single glazing are just that, subjective – and not a little academic. What is behind a window – be that curtains, blinds, secondary glazing, lighting, etc – will have infinitely more visual impact on the glazing than the type and arrangement of the clear glass/glazing itself, be that single or double glazing or sheet or float glass.

To demonstrate what I am alluding to here, on Sunday I took some photographs of the window and glazed door assemblies to the main rear facade at our house at 38 Ludlow Road, which are attached herewith for your reference. The first floor window – which is single glazed – incorporates the Society’s precious secondary glazing behind, in which regard the reflection of the glazing bars, mullions and transoms of the main window in the secondary glazing is clearly apparent and obvious. The glazed doors below – wherein the key timber sections, including glazing bars, are as those to the window assembly above – incorporate slim sealed double glazing units, which are in keeping, integrate discretely and elegantly with the surrounding sections and are in no way visually incongruous, unlike the reflection situation applying to the window above. I know what visual impression I find the more pleasing and less disruptive.

I do question if the Society – in propounding their views regarding slim double glazing units – have given any balanced consideration to the real gambit of variables which influence the external appearance of Brentham Windows. It seems not, otherwise I doubt that the Brentham News Extra April 2015 article would have been penned as it was. Peddling such misleading information and packaging it up to give the impression of it being fact does the Society little or no credit whatsoever.

It is not my intention to argue the pros and cons of the two Appeal Decisions referred to in the broadsheet in any great detail, other than to point out that the reason for dismissing the 21 Denison Road Appeal – as it related to the windows to the front facade – related to the colour (black) of the edge seals/spacers to the proposed double glazed units and the 9mm increase in depth apparently attaching to the glazing bars and relative to the depth of the original glazing bars to the windows on the Estate, whilst the proposals attaching to the upheld Appeal in respect to the replacement windows to the front (and rear) facade at 4 Denison Road allowed for white edge seals/spacers, with only slightly deeper glazing bars to accommodate the double glazing. The Appeal Inspector concluded that neither the slightly deeper glazing bars nor any reflective difference attaching to the double glazing units would be discernable even when seen at an oblique angle from the road.

Over the coming year, more and more properties on the Estate will need – for one reason or another – to have their windows replaced, in all or in part. Rather than trying to resist the inevitable with contrived and creative arguments concerning slim double glazing units, I am of the firm opinion that the Society, along with the Advisory Panel, should be addressing the matter positively, objectively and rationally – and if this means proper and balanced consultations on the subject so be it. Regarding secondary glazing as the answer before you really know precisely what the question is doesn’t help a great deal.

Incidentally – and despite what is reported in the broadsheet – incorporating sealed double glazing does not have to mean the total replacement of existing/original window assemblies to facilitate. The openable and fixed lights/casements would essentially need to be replaced, but the surrounds – jambs, heads, cills and mullions – could be retained and be modified/routered out to accommodate the slightly deeper casements.

The future and the conservation of this wonderful Estate is of course of primary importance, but please remember that – in building heritage terms – Conservation means the careful management of change, not pickling.

As someone who has recently undergone a complete refurbishment of our Brentham house, I would like to register my disappointment with the intransigent view of ‘The Brentham Society’ regarding the double glazing v secondary glazing issue. I thought those who had paid their subscriptions (and sometimes more), were all members of The Brentham Society. As such, it would be nice to have been consulted, or at least given the opportunity to discuss the views of others who may represent us.
I have previously, elsewhere on this site, expressed my opinions about double glazing with respect to maintaining the visual integrity of the houses and the commendable foresight of George Lister Sutcliffe in incorporating the most up to date features into his house designs. By only advocating the installation of secondary glazing with its double reflections and the poor visual impact, those who are charged with upholding our heritage in Brentham do a disservice to the rest of us who want a warm and quiet home in this, the best part of West London.
I can also confirm that the new double glazed windows in our side and rear extensions, as well as the new french doors are fully compliant with current Building Regulations as required by the Planning Permission. Only the original front windows allow the heat to escape. If there is any doubt about the visual qualities of Slimlite units compared with the originals, we have both and are happy to demonstrate the qualities for the benefit of all Brentham residents.

I am rather perplexed by the newsletter that stated how the windows should be kept as they are but also should have rather ugly, inefficient and ineffective secondary glazing. Surely this is contradictory. The society seems to recognize that we should be allowed to do something to alleviate the condensation, heat retention and noise issues, and are suggesting that we should denigrate the look of the estate to do so rather than going with the superior and greatly preferred route of getting properly constructed slimline double glazing.
What the society needs to do is protect our estate from deteriorating, to keep its character. And we are all the society, trying to maintain a high standard: none of us wants to live in a run-down area. So we, the society, have to find out how the preferred method of slim line double glazing can be best fitted, best specified to continue the high standard.
Double glazing has now been approved in one notable instance, at 4 Denison Road, and in many others where there have been extensions. If there is not to be a clash of interests, a civil war of sorts, we have to work for the whole estate to benefit from the maintaining the current look with slimline double glazing instead of spoiling it with secondary glazing.
Could we please have an official statement to that intent. Stating otherwise would just cause resentment and discontent where individuals will have to go thought laborious and torturous mounds of paper to get individual permissions for each house. With the official statement, we will all benefit from a consistent approach we can all be behind.
I look forward to the meeting on the 30th where I hope some double glazing options will also be shown, if only so the doubters can point out exactly what’s wrong with them and their reflections compared to the dual reflections of secondary glazing.

Editors note: In response to the comment below about Slimlite double glazing units conforming to current new building regulations, we have confirmed with the Glass and Glazing Federation that Slimlite 4x3x4mm units, with a stated U-value of 2.1, do not conform with the Building Regulations for new build

Why are you only referencing 4:3:4 Slim double glazing units when other build ups such as 4:5:4, 3:4:4, 3:6:4 etc etc achieve much better U Values and comply with Building Regulations Requirements? Once again the Brentham Society are being creative with their feedback regarding double glazed units.

The duty of the Brentham society is to comment responsibly, objectively
and accurately on matters that affect all residents and members. This
document (BN Extra April 2015) contains so many factual inaccuracies and so much biased
opinion that you should be ashamed of it. Either the main author has
done little or or no research, or is at best being disingenuous, or is
being downright economical with the truth in support of an opinion not
shared by many in the Society.

The section titled “Double glazing in Brentham frames” contains a number
of blatant errors and untruths. I can state for a fact that, for
example, Slimlite double glazing units conform to current new building
regulations, can be fitted to existing Brentham frames with minor
modification and do not require glazing bars that differ in any way on
overall dimensions, including depth, from traditional Brentham windows.

I can assure the authors from recent experience that the councils
planning official were unable to spot the difference in the use of these
units from less than 5 metres away.

If your document was at all objective, it would not state as a fact that
“primary double glazing, even of the slim type, does affect the
appearance of a house”. That is an opinion of your author, not a fact.
it is aa statement designed to confuse different methods of primary
double glazing in the minds of less informed readers.

I would suggest that you have a duty to issue a newsletter containing
corrections to the incorrect facts that this document contains. It might
no correct the bias, but at least the conversation can be cariied
forward based on facts and not opinion.

As a member of the Brentham society, even contributing more than the
base subscription, I am appalled that members money is being wasted on
propaganda such as this. By all means, let’s have the debate, but do it
in a constructive and factual manner. as it stands, this is junk mail.

In the above document you state “As you walk around our estate, probably the most distinctive features you see on the front of Brentham houses are the windows. Their appeal rests in the delicacy of the frames and glazing bars and the characteristic uneven reflections created by the original glass panes”.

Really? As I walk around our estate, the most distinctive features that I and I am sure others see, are numbers of rotting, unpainted and dirty windows, flaking paintwork; poorly kept gardens; overgrown hedges (some of which prevent you from even seeing the house); trees that are far too large that block pavements; and tree roots either protruding above the pavement level or lifting pavings from below. I wonder very much whether any of us, apart from certain members of the Brentham Society, really see or worry about the ‘characteristic uneven reflections created by the original glass panes’.

If you really want to do something about preserving the special character of our suburb, do something positive about issues like those indicated above instead of making life difficult for those who are genuinely trying, in their own way, to do so.

Secondary-glazed windows stick out like a sore thumb and it’s no wonder that with the intransigence shown by the members of the Brentham Society towards slim-line double glazing some people have ignored the guidelines and gone it alone. The windows at 4, Denison Road look lovely and no-one would know they were double-glazed unless they stood right next to them. If they are a compromise they’re a very good one, particularly as many residents on this estate are crying out to be able to double glaze their windows. This needs to be recognized by the Brentham Society and they should be helping all of us, not just the stick-in-the-muds who wouldn’t recognize a good thing if it hit them in the face. We don’t live in a museum – or do we?

A Brentham resident gave me the name of a firm called Magneglaze who supply acrylic secondary glazing panels cut to your specification. They have fitted them successfully (it’s a DIY job) and they don’t show from the outside. I’ve since discovered another company, Ecoease, who use PET clear plastic sheets. These are rated Class 1 Fire Retardant, whereas acrylic is only Class 3. I have been thinking of installing some of these panels on some windows. Does the Committee have any views on these? If they are allowed and enough residents are interested perhaps we could get a discount (and someone to do the measuring and fitting). See details on their websites.